This invention relates generally to bridge footings and abutments, and particularly to portable footings and abutments that can be used in areas of unsatisfactory soil or water table conditions.
Typical bridge footings are constructed on soils that have adequate bearing capacity for the bridge loads that must be carried. The footings are made of reinforced concrete and are intended to have little or no settlement so they can provide the bridge superstructure with a support of constant elevation.
To build a bridge in areas where soil conditions have inadequate bearing capacity, the poor soils are removed and replaced with better soil and well-draining stone. If the area has a high water table, the footings must be formed on top of suitable piles or caissons that transfer bridge loads down to suitable soil or even bedrock. Of course, these additional structures are expensive and time-consuming to build. When they are built in wetlands, additional regulatory approval may be necessary before the bridge can be built.
When soil improvements are necessary, their cost may be prohibitive, especially when the bridge is small or intended to only carry small loads such as small vehicle or foot traffic.
Further, when bridges are no longer necessary or they need repair, it is necessary to perform extensive deconstruction that has a traumatic impact on surrounding wetlands.
Thus, there is a need for an improved bridge footing that can be used for smaller bridges when soil conditions are inadequate, removed when there is no longer a need for the bridge, and used in areas that require minimal environmental impact.
The present invention overcomes the deficiencies in prior art bridge footings and abutments. The present invention can be used to distribute bridge loads evenly over the soil and permit some vertical displacement from varying water levels and frost heave.
Load distribution is effected by one or more legs that transfer loads downward to a bearing plate. The bearing plate bears on a large area of soil to distribute loads more widely than a typical bridge footing to provide the proper bearing capacity. As water levels rise and fall during the freeze and thaw cycles, the bearing plate and legs minimize the obstruction to water flow under the bridge and they change bridge elevation with the surrounding soil with no adverse consequences for the bridge.
Lateral movement of the bearing plate is restrained by a pipe that is driven deep into the soil. The pipe extends upwardly through a mating hole in the bearing plate to resist lateral movement of the bearing plate, legs, and bridge deck.
Such a bridge footing or abutment can be prefabricated, is inexpensive to install, is suitable for use in small load bridges, and can be removed when the bridge is no longer necessary, all without excessive adverse environmental impact.